Numerical NEGF-Based Study of Urbach Tails in III-V Materials and Superlattices

Numerical simulations that use the non-equilibrium Green's function (NEGF) method applied to an 8-band k.p Hamiltonian were performed for exemplary III-V material and superlattice with the intent to examine an influence of scattering processes on the formation of band tails. Results reveal that the Urbach parameter is not directly proportional to the value of perturbing potential but rather to its logarithm. It effects in a much modest temperature dependence of this parameter, which was reported in the literature for several III-V compounds. The values of the absorption coefficient estimated in the paper also remain in reasonable agreement with the experimental data reported in the literature for the bulk InAs and type-II InAs/InAsSb superlattice (SL).